Fluorescence Measurements on Functionalized Polymer Surfaces—Problems and Troubleshooting K ATRIN H OFFMANN ,R ENATE M IX ,U TE R ESCH-G ENGER , AND J OERG F. F RIEDRICH Federal Institute for Materials Research and Testing (BAM), Div. I.5, Berlin, Germany Plasma-chemically tailor-made polymer surfaces are of ever-increasing importance to control surface properties in material science, as well as for (bio)analytical and biomedical applications. For the characterization of such systems, sensitive fluorescence techniques are attractive tools. To underline the potential and drawbacks of these strategies, this article addresses different problems that complicate fluorometric analysis. To overcome some of these limitations, such as nonspecific adsorption of unreacted fluorescent probes, we discuss potential troubleshooting, including the use of a chromogenic and fluorogenic pyrylium dye for the detection of amino functionalities at polypropylene surfaces. Key words: fluorescence spectroscopy; polymer functionalization; surface labeling; pyrylium label Introduction Functionalization of polymer surfaces with OH, NH 2 , or CHO groups by, for example, plasma chem-ical modification allows control of the hydrophilicity, as well as the adsorption and wetting properties of polymeric surfaces and provides the basis for the at-tachment of bio- and sensor molecules. 1 , 2 Crucial for all applications of these tailor-made polymeric materi-als is the characterization of the type and the density of reactive functional groups at the surface. Commonly used surface-sensitive techniques such as X-ray photo-electron spectroscopy and attenuated total reflection Fourier transform infrared spectroscopy are expen-sive, provide only the elemental composition of a 5-to 7-nm-thick surface layer, or are limited to a surface layer with a thickness of 1.6–2.5 µ m 3 ; they often fail at low concentrations of surface functionalities. Thus, the application of straightforward labeling techniques in combination with simple fluorometric methods be-comes attractive. 4 Despite the obvious potential of fluorometry, there have been only a few examples reported for the charac-terization of surface functionalities on (bio)analytically relevant supports. 4–10 Fluorometric characterization of Address for correspondence: Dr. Katrin Hoffmann, Federal Institute for Materials Research and Testing (BAM) I.5 Bioanalytics, Richard-Willst¨atter-Str. 11, D-12489 Berlin-Adlershof, Germany. Voice: + 030-8104-5878; fax: + 030-8104-5005. katrin.hoffmann@bam.de surface functions is complicated by different factors, 8 , 11 including nonspecific adsorption, 8 an inhomogeneous dye distribution or penetration of dye molecules into polymers, 12–14 dye–dye and dye–matrix interactions, and the sensitivity of the fluorophore’s spectroscopic properties to the microenvironment. 25

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